Optical device and method of manufacturing the same

ABSTRACT

An optical device includes a light transmitting non-linear optical material having a first face and a second face. The first and second faces oppose each other. The first face has a plurality of first reflecting portions provided thereon, and the second face has a plurality of second reflecting portions provided thereon. Each of the second reflecting portions corresponds to one of the first reflecting portions. Furthermore, the first and second faces are substantially flat except for at least one convex arcuate portion being formed on at least one of the first and second faces. Additionally, at least one of the first and second reflecting portions is obtained by coating a reflective material on the convex arcuate portion.

This application is a X continuation, of application Ser. No. 08/466,990filed on Jun. 6, 1995, now abandoned; which was a divisional ofapplication Ser. No. 07/901,029 filed on Jun. 19, 1992 now U.S. Pat. No.5,999,325.

BACKGROUND OF THE INVENTION

This invention relates to an optical part or an optical device, andparticularly to an optical part or an optical device having an opticalmaterial on which minute, generally spherical or aspherical convex orconcave arcuate faces are formed and a process of producing the same.Further, the present invention relates to an optical device having anoptical path of a great length such as, for example, a higher harmonicwave converting device and a short wavelength laser apparatus employingsuch optical device.

Conventionally, as a laser resonator, a laser resonator is known of thestructure wherein a pair of concave reflecting mirrors are disposed inan opposing relationship to each other on the opposite sides of a lasermedium. One of the reflecting mirrors is a total reflecting mirror whilethe other reflecting mirror is a mirror which passes part of laser lighttherethrough. In order to miniaturize such a laser system, it isnecessary to make the spacing occupied by the reflecting mirrors assmall as possible. Further, as miniaturization of systems proceeds, itis necessary to decrease the distance between the reflecting mirrors.

Meanwhile, non-linear optical devices are used which convert a frequencyof light making use of a non-linear mutual action of light waves in asubstance. The non-linear mutual action may be, for example, productionof a second harmonic wave, optical parametric oscillation, production ofa difference frequency or the like. Such an optical device isconstituted from an optical resonator consisting of two such concavereflecting mirrors as described above, and an optical material in theform of non-linear optical crystal placed between the concave reflectingmirrors. A microlens, which is one of optical parts, is used for anoptical communication system or optoelectronics. Since light emergingfrom a laser or an optical fiber spreads at the angle of 10 to 40degrees or so, the microlens is used to convert such light into parallellight or further converge such light into a small spot. As one ofmethods of producing a microlens, there is a method wherein a maskpattern having a necessary circular opening is formed on a glasssubstrate using the technique of photolithography and ion exchanging isperformed through the opening so that the refractive index of a portionof the glass substrate corresponding to the opening is made differentfrom that of the other portion of the glass substrate.

While various optical devices are described so far, if such opticaldevices can be manufactured by forming a convex arcuate face integrallyon an end face of an optical material, then this is very advantageousfor miniaturization of an apparatus and so forth. By the way, if it isattempted to form a spherical or aspherical convex arcuate face on asurface of an optical material, one of most popular methods is a methodby polishing. Accordingly, it is possible to work only one or severalworks, and consequently, optical devices cannot be manufactured in amass at a low cost. Further, where such polishing is involved, there isa problem that, from a physical restriction, a plurality of convexarcuate faces cannot be formed in the proximity of each other on asurface of an optical material. A Fresnel lens is known as an example ofan aggregate of small lenses. In this instance, since an electron beampicture drawing apparatus is employed for production of a Fresnel lens,the equipment is very expensive and the mass productivity is low.Further, while it is possible to manufacture, by molding, a microlens onwhich a plurality of convex arcuate faces are provided, the material ofthe microlens is limited to such material that is suitable for molding.Accordingly, there is a problem that it is impossible to manufacture amicrolens using such a material as a single crystal material or a highmelting point amorphous material.

By the way, since generally a laser is limited in output wavelength,there is a method wherein laser light is converted into coherent lightof another wavelength making use of a non-linear optical phenomenon inorder to obtain laser light of a shorter wavelength. As a representativeexample of the same, there is a method wherein laser light is convertedinto a higher harmonic wave by means of a higher harmonic wave generator(SHG). This depends upon the fact that, if laser light of a frequencyω_(o) is introduced into crystal of a non-linear medium, then light ofthe frequency 2ω_(o) is outputted from the crystal. Such higher harmonicconversion has been attempted in accordance with various methods, and itis known that a higher harmonic output thus converted increases inproportion to an input power to the second power or an internal power tothe second power of a resonator and a length to the second power of thenon-linear medium (however, at an optimum focus, the higher harmonicwave output increases in proportion to a length of the non-linearmedium). Accordingly, in order to increase the higher harmonic waveoutput, it is necessary to, increase the internal power or the length ofthe non-linear medium.

As a method for higher harmonic conversion which is conventionallyemployed, there is a method of direct conversion wherein non-linearcrystal is cut into a piece, and low reflection coatings are applied tothe polished opposite end faces of the non-linear crystal piece, andthen exciting light is irradiated upon the non-linear crystal piece.With the present method, direct conversion making use of a semiconductorlaser is possible, but since generally it is difficult to obtain a longnon-linear crystal piece, there is a problem that the available higherharmonic wave output is very low. Further, there is another methodwherein a non-linear medium is disposed in a laser resonator. With thepresent method, since the internal power of the resonator can be madeequal to 100 times or so the intensity of incidence light readily, acomparatively high higher harmonic output can be extracted. However,there are problems that the system is complicated and that a separatemodulator is required because direct modulation by the semiconductorlaser is not performed. Further, as a method which efficiently raisesthe incidence power and artificially satisfies a phase matchingrequirement, there is a method wherein exciting light is enclosed bymeans of a waveguide structure to effect higher harmonic conversion. Themethod, however, has problems that technical difficulty is involved inproduction of the waveguide and besides that it is very difficult tointroduce exciting light into the waveguide and efficiently extract ahigher harmonic wave from the waveguide. Also, there is a problem that,since it is difficult, from a restriction in manufacture, to obtain asymmetrical structure with respect to an optical axis and consequentlyit is actually difficult to extract a higher harmonic wave of a singlemode, it is limited in application.

As described so far, with the methods proposed till now, the output istoo low, and if the case is considered wherein an optical device is usedas a light source, for example, for an optical disk, then the situationis such that it is difficult to provide a light source device which hasa higher harmonic wave output of 1 mW or so and can effect simplemodulation.

By the way, a solid-state laser which is longitudinally excited by alaser diode can present a high gain due to a wide spectrum and pumpinghaving a spatial characteristic. Various laser devices of the highoutput type (including multi-facet pumping devices, LD multiplexingdevices and fiber bundle pumping devices) have been developed till now.However, in order to scale up the longitudinal excitation to increasethe output power, generally it is necessary to make a cavity large sothat the laser device may stand a higher basic mode. Further, if thelongitudinal excitation is scaled up, then the gain is decreased due todouble refraction or aberration which is caused by heat.

On the other hand, as a method for scaling up the longitudinalexcitation while keeping the cavity compact, there is a method wherein,making use of a thermal lens effect which is caused by exciting lightintroduced into a solid-state laser medium, a pair of flat mirrors aredisposed on the laser medium so that multi-array excitation may takeplace (Oka, M. et at. CLEO '91, p.40). However, this method has problemsthat, since it makes use of a thermal lens effect, the threshold levelin laser oscillation is high and the oscillation efficiency is low.

SUMMARY OF THE INVENTION

1. Optical Device of the Invention

In the present invention, an optical device which has an opticalmaterial having a convex arcuate face or a concave arcuate face formedon a surface thereof includes not only an optical device which includes,as one of components thereof, an optical material which has a convexarcuate face or a concave arcuate face formed on a surface thereof, butalso an optical device which is constituted only from an opticalmaterial which has a convex arcuate face or a concave arcuate faceformed on a surface thereof.

Such an optical device is, for example, a laser array or a microlens orthe like which has an optical material which has, for example, aplurality of concave or convex arcuate faces formed on a surfacethereof.

Further, an optical device can be listed wherein, as shown in FIG. 7, aconvex arcuate face is formed integrally on one of a pair of end facesof a laser medium or a non-linear optical material while the other endface of the laser medium or the non-linear optical material is formed asa flat face. In this instance, a total reflecting mirror or asemi-transmitting film may be coated on one or both of the convexarcuate face and the flat face of the laser medium or the non-linearoptical material. It is to be noted that, while the other end face ofthe laser medium or the non-liner optical material extends in parallelto the one end face in FIG. 7, in the case of an optical device of thering laser type (optical device of the type wherein a polygonal opticalpath is formed in the material), the other end face may be inclined withrespect to the one end face as shown in (b) of FIG. 18.

Junction type laser resonators shown in FIGS. 12 and 13 can beconstructed using such an optical device. In FIGS. 12 and 13, referencenumeral 13 denotes a total reflecting film for light, and 14 asemi-transmitting film for light.

Further, the present invention provides an optical device which ischaracterized in that, as shown in FIG. 6, a first convex arcuate faceis formed integrally on an end face of a laser medium while a secondconvex arcuate face is formed integrally on the other end face of thelaser medium, and a total reflecting film which totally reflects laserlight is provided on the first convex arcuate face while asemi-transmitting which reflects part of laser light and transmits partof the laser light therethrough is formed on the second convex arcuateface, thereby to constitute a laser resonatoor Such an optical deviceconstitutes a laser resonator in a laser apparatus of the arcay typewhich will be hereinafter described.

Further, as described in the section of “3. Optical Device Having ZigzagOptical Path” hereinafter described, the present invention provides anoptical device characterized in that it is composed of a lighttransmitting optical material having a first face and a second faceopposing to each other and has a plurality of first reflecting portionsprovided on the first face and a plurality of second faces provided onthe second faces individually in an opposing relationship to the firstreflecting portions and besides has a zigzag optical path which isprovided between the first reflecting portions and the second reflectingportions and alternately couple the first reflecting portions and thesecond reflecting portions to each other, and each of at least ones ofthe first reflecting portions and the second reflecting portions is areflecting portion formed by coating a reflecting film on a convexarcuate face. The present invention further provides a short wavelengthlaser apparatus which employs such optical device.

Preferably, the convex arcuate face or concave arcuate face is agenerally spherical face or aspherical face, for example, a face of anellipsoid of revolution. In this instance, the spherical face oraspherical face may have distortion wherein the radius of curvature in aradial direction varies continuously or stepwise.

A first method of forming at least one convex arcuate face or concavearcuate face on a surface of an optical material is achieved by a methodcharacterized in that at least one convex arcuate face or concavearcuate face is formed by photolithography on a photoresist film formedon a surface of the optical material, and the surface of the opticalmaterial and the photoresist film are etched to form, on the surface ofthe optical material, at least one convex arcuate face or concavearcuate face similar to the convex arcuate face or concave arcuate faceof the photoresist film.

Here, as a first method of forming a convex arcuate face or concavearcuate face by photolithography, a method is first listed wherein, atthe exposing step of exposing the photoresist film to light of acircular or elliptic pattern, the intensity of the exposure light isgradually varied from the center to an outer periphery of the pattern.

Here, to gradually vary the intensity of the exposure light from thecenter to an outer periphery of the pattern includes a case wherein thecolor is white (transparent) at the center and becomes dark (opaque)toward an outer periphery and another case reverse to this.

As such method, for example, the following methods can be listed.

(1) A method wherein, using a lens having a low resolution such as anenlarger for a photograph film as an exposure lens, light of a circularor elliptic pattern of a photomask is focused on a photoresist film toeffect exposure of the photoresist film and then the photoresist film isdeveloped.

(2) A method wherein a circular or elliptic pattern to be formed on aphotoresist film is focused in a fully defocused condition on aphotoresist film to effect exposure of the photoresist film and then thephotoresist film is developed.

(3) A method wherein, when a photoresist film is to be exposed to lightusing a photomask having a pattern formed thereon, a white or blackcircular or elliptic shape is photographed in a somewhat defocusedcondition to obtain a negative film having a circular or ellipticpattern which varies in photographic density from a central portion toan outer periphery thereof, and using the negative film as a negativefor transfer of a circular or elliptic pattern, an image of the negativefilm is formed on a photoresist film or a photoresist film is exposed tolight in a condition wherein the negative is positioned in the proximityof or in close contact with the photoresist film, whereafter thephotoresist film is developed.

(4) A method wherein a diffuser is inserted intermediately of an opticalsystem for exposure to obtain diffused light, and an image of a patternto be formed is formed on a photoresist film with the diffused light toeffect exposure of the photoresist film, whereafter the photoresist filmis developed.

A diffuser is an optical element which is obtained by sand-blasting asurface of an optical glass element such as BK-7 using abrasive grain ofalumina and diffuses light, and, for example, DFSQ-50C02-1500 producedby Siguma Koki and so forth can be listed as such.

(5) A method wherein a photoresist is exposed to light in a conditionwherein a photomask on which a pattern is formed is spaced away from thephotoresist film so as to provide a distance between them and then thephotoresist is developed.

(6) Either of a convex arcuate face and a concave arcuate face can beformed depending upon whether the pattern of the photomask is black orwhite in any of the methods (1) to (5) described above.

Further, as a second process of the present invention, there is a methodcharacterized in that a photoresist film of a circular column-shaped orelliptic column-shaped pattern is formed by exposure based onphotolithography and development on a photoresist film formed on asurface of an optical material and having a generally flat and smoothupper end face, and the photoresist film is heat treated to deform thegenerally flat upper end face of the photoresist film into a convexarcuate face, and then the surface of the optical material and thusdeformed photoresist film are etched to form at least one convex arcuateface similar to the convex arcuate face of the photoresist film on thesurface of the optical material.

In other words, if a photoresist film is exposed to light using aphotomask having a circular or elliptic pattern formed thereon and isthen developed, then if focusing upon exposure is appropriate. then acircular column-shaped photoresist film having a generally flat andsmooth upper end face is formed on the surface of the optical material.Thus, if the circular column-shaped or elliptic column-shapedphotoresist film is held at a temperature higher than a glass transitionpoint of the material constituting the circular column-shaped orelliptic column-shaped photoresist film so that the photoresist film maybe fluidized by heat, then an upper end corner portion of the circularcolumn-shaped or elliptic column-shaped photoresist film is deformedround until the circular column-shaped or elliptic column-shapedphotoresist film is rounded by its surface tension and is deformed intoa convex arcuate face as a whole.

In the foregoing, preferably etching is performed by dry etching. Gas tobe used in etching can be determined suitably depending upon an opticalmaterial employed. Conditions of etching depend upon a profile of aconvex arcuate face or a concave arcuate face to be formed on a surfaceof an optical material. In the case of dry etching, some distortion canbe provided to the convex arcuate face or concave arcuate face bychanging the sectional shape of the convex arcuate face or concavearcuate face to be formed on the surface of the optical material (thesectional shape in a direction perpendicular to the surface of theoptical material) by continuously or stepwise changing, at any timeduring etching, the kind, amount or flow rate of gas used, the highfrequency output. the intensity of a magnetic field for enclosure, theaccelerating voltage for gas ions, the etching time or the like.

It is to be noted that, in the case of an optical device wherein laserlight is reflected by an upper face, a lower face or the like in amaterial in order to form many optical paths in the inside of thematerial such as a ring laser, preferably the face is made a fault-freemirror face in order to obtain a high reflection factor. As hereinafterdescribed, in the present invention, when an optical material which hasonly one lens (convex arcuate face or concave arcuate face) on a surface(one end face) thereof is to be manufactured, a method is employedwherein, for example, a plurality of convex arcuate faces are firstformed on the optical material and then the optical material is cutalong a border around each of the convex arcuate faces. In thisinstance, since a cut face makes, with an optical device of the ringlaser type, a reflecting face for light, it is necessary to polish itinto a mirror face by means of polishing abrasive grain or the like.However, a mirror face obtained by polishing by means of abrasive grainis not free from a fault but has fine faults caused by the abrasivegrain. Since such faults deteriorate the reflection factor for laserlight, according to the present invention, faults on a polished face areremoved in the following method. First, a photoresist film is formed ona faulty polished face similarly as the case of a convex arcuate face ora concave arcuate face, and then dry etching is performed for thephotoresist film and the optical material until the faults disappear.While, in the case of an optical device of the ring laser type, if anupper face or a lower face (or side face) is not a cut face, it isnecessary to polish a face serving as a reflecting face (except a coatedface) into a mirror face, also in this instance, a fault-free mirrorface can be obtained by applying the fault removing method describedabove.

An action of an arcuate face being formed on an optical material in sucha manner as described above will be described. First, describing thecase wherein a convex arcuate face is formed, a photoresist film havinga convex arcuate face is formed on a surface of an optical material onwhich a convex arcuate face is to be formed. By etching, the opticalmaterial which is not covered with the phGtoresist film begins to beetched immediately. The photoresist film before etching has the convexarcuate face, and accordingly, the thickness of the photoresist filmbecomes greater toward a central portion of the same.

Therefore, a peripheral portion of the photoresist film is etchedearlier than a central portion of the photoresist film, and accordingly,the optical material positioned below such peripheral portion is etchedearlier and by a higher rate than the optical material positioned belowthe central portion.

As a result, a convex arcuate face similar to the convex arcuate face ofthe photoresist film is formed on the surface of the optical material.In this instance, if etching is performed by dry etching and conditionsof the dry etching are varied continuously or stepwise at any timeduring etching, then a convex arcuate face having some distortion isformed. When an optical material having only one lens integrally at anend face thereof is to be manufactured, a method can be listed wherein aplurality of convex arcuate faces are first formed on an opticalmaterial and then the optical material is cut along a boundary aroundeach of the convex arcuate faces. When there is the necessity of makinga cut face a mirror face, if the cut face is polished into a mirror faceby means of polishing abrasive grain or the like and then a photoresistfilm is formed on the polished face and then dry etched, also the cutface is etched uniformly, subsequently to the photoresist film, so thata fault-free mirror face is formed.

When a concave arcuate face is to be formed, the thickness and so forthof a photoresist film are reverse to those of the case of a convexarcuate face.

In the present specification, an optical device signifies any of a laserresonator, a monolithic laser system, a non-linear optical device, amicrolens, a ring laser, an optical device having a zigzag optical path,which will be hereinafter described, and so forth.

In case the optical device is a laser resonator, the optical material iscomposed of a laser material and a surface of the optical device onwhich a convex arcuate face is formed is an end face which reflects atleast part of laser light.

In case the optical device is a plurality of laser resonators disposedin an array, the optical material is composed of a laser material and asurface of the optical material on which a plurality of convex arcuatefaces are formed is an end face which reflects at least part of laserlight.

In case the optical device is a non-linear optical device (which may beof the type similar to a ring laser), the optical material is composedof a non-linear crystal material and a surface of the optical materialis an end face which has one or a plurality of convex arcuate facesformed thereon and reflects at least part of laser light. The other endface of the optical material extends in parallel or In an inclinedrelationship to the surface (one end face) of the optical material.

In case the optical device is a microlens, the optical material iscomposed of an amorphous material such as glass or a crystal materialsuch as quartz and one or a plurality of convex arcuate faces are formedon a surface of the optical material.

As the optical material, laser materias such as Nd:YAG, Nd:YAB,Nd:Y₃Al₅O₁₂, Nd:YLiF₄, Nd:YVO₄, Nd:La₂Be₂O₅ and Nd:Y₃Al₃(BO₃),non-linear materials such as KNbO₃, LiNbO₃ and KTiOPO₄, amorphousmaterials such as BK7, composite quartz and glass and crystal materialssuch as quartz, calcite, silcon and GaAs can be listed.

As a photoresist, preferably a photoresist obtained by polymerization ofa diazo photosensitive material with a phenol resin generally calledpositive type photoresist is employed.

It is to be noted that a convex arcuate face in the present inventionincludes an independent convex face and two or more convex faces whichpartially connect to each other. A concave arcuate face in the presentinvention includes an independent concave face and two or more concavefaces which partially connect to each other.

According to the present invention, a large number of very small,generally spherical or aspherical convex arcuate faces or concavearcuate faces can be formed collectively on a surface of an opticalmaterial, and further, a plurality of convex arcuate faces or concavearcuate faces can be formed in the proximity of each other. Accordingly,a novel optical device such as a very small solid-state laser, a ringlaser, a solid-state laser of the array arrangement, a microlens or anon-linear optical device which has a very small solid-state elementwhich was not able to be manufactured by conventional polishing can bemanufactured readily in a mass at a low cost. Further, it is possiblefor the spherical face or aspherical face to have arbitrary distortionin accordance with the necessity. Further, the reflection factor of aface for which polishing into a mirror face has been performed can beenhanced by removing faults after polishing.

2. Array-Type Laser Apparatus Employing Optical Device Having ConvexArcuate Face

An optical device wherein a plurality of convex arcuate faces are formedon a laser medium can be used as a laser resonator in order toconstitute an efficient multi-array type laser. In particular, an arraytype laser apparatus can be provided which is characterized in that itcomprises plurality of exciting sources for laser oscillation, and alaser resonators wherein a plurality of convex arcuate faces are formedon at least one end face of a solid-state laser medium and each of atleast ones of the convex arcuate faces and other end end faces of thesolid-state laser medium opposing to the convex arcuate faces is coatedwith a reflecting film.

A plurality of exciting light beams outputted from the exciting sourcesare introduced into the plurality of convex arcuate faces formed on theend face of the solid-state laser medium. The exciting light beamsintroduced into the laser medium through the convex end faces arerepetitively reflected by the coatings applied to the opposing face andthe face through which the exciting light beams are introduced. In thisinstance, each of the convex arcuate faces acts as a concave reflectingmirror, and the laser medium itself functions as a stable type laserresonator so that multi-array type oscillation occurs.

Normally, as stable type laser resonators, a stable type laser resonatorof the structure wherein a pair of concave reflecting mirrors aredisposed in an opposing relationship to each other on the opposite sidesof a laser medium and another stable type laser resonator of thestructure wherein a concave reflecting mirror is disposed on one side ofa laser medium and a flat mirror is disposed on the other side of thelaser medium in an opposing relationship to the concave reflectingmirror are known. One of the reflecting mirrors is a total reflectingmirror, and the other reflecting mirror is a reflecting mirror whichpasses part of laser light therethrough.

In order to miniaturize such a laser system, it is necessary to minimizethe spacing occupied by the reflecting mirror. Further, as theminiaturization of a system proceeds, the distance between thereflecting mirrors must necessarily be reduced.

If a laser resonator can be manufactured by forming a convex arcuateface integrally on a solid-state laser medium, then this is veryeffective for miniaturization of an apparatus and particularlyadvantageous for a high density array type laser.

If the opposite end faces of a laser medium wherein a convex arcuateface is formed on one or both of the opposite end faces in such a manneras described above are each coated with a film which reflects light,then the laser medium can function as a laser resonator. The side of thelaser medium into which exciting light is introduced is provided withsuch a coating that transmits exciting light therethrough but reflectsalmost all of laser light emitted from the solid-state laser medium, andthe output side of laser light is provided with such a coating thatreflects almost all of exciting light but transmits part of amplifiedlaser light therethrough.

As a method for such coating, a method wherein two kinds of thin filmshaving different refractive indexes are layered, by vacuum deposition orsputtering, alternately to such thicknesses with which the respectiveoptical lengths at an aimed reflecting wavelength correspond to the ½wavelength can be listed.

While a krypton arc lamp, a xenon flash lamp or the like can be used asan exciting source for the laser resonator, a semiconductor laser ispreferable from the point of view of reduction in power, enhancement inefficiency, miniaturization and so forth. Particularly, as an excitingsource for an array type laser, it is preferable for the object ofsimplification of an apparatus to employ a semiconductor laser of themulti-stripe type which outputs a plurality of laser beams, for example,a laser diode of the multi-stripe type.

In this manner, if an exciting source which emits a plurality of laserbeams is employed, then it is only necessary to form convex arcuatefaces on an end face of a laser medium corresponding to such pluralityof laser beams, and accordingly, construction of an apparatus can besimplified remarkably.

However, even a laser apparatus which outputs a single laser beam suchas a krypton arc lamp, a xenon flash lamp or a semiconductor laser ofthe single type can be employed as the exciting source described abovein the present invention, and in this instance, an optical fiber forguiding a laser beam outputted from each of the laser apparatus may besuch that it is inputted to a corresponding one of the convex arcuatefaces.

The wavelength of the exciting light source must necessarily coincidewith or be in the proximity of an absorption spectrum of the lasermedium. In case a laser diode is employed as the exciting source, forexample, if a laser diode which oscillates in the proximity of anabsorption wavelength of the laser medium and then the temperature isvaried so that the absorption may be maximum to effect tuning, then thewavelength of the exciting light source can be made coincide with theabsorption spectrum of the laser medium. In case Nd:YAG is employed asthe laser medium, a GaAlAs semiconductor laser can be listed as apreferable exciting source.

A laser apparatus of the array type of the present invention isconstituted by disposing a solid-state laser resonator and an excitingsource such that exciting light may be converged to a convex arcuateface formed on the solid-state laser resonator. Since exciting lightoutputted from an exciting source is emitted normally with a fixedangle, when a plurality of laser beams emitted from individual activewaveguides of a laser diode of the multi-stripe type are to beintroduced into the individual convex arcuate faces formed on thesurface of the solid-state laser medium, a focusing lens may beinterposed in accordance with the necessity. The plurality of laserbeams are converted into parallel beams of light or converged into aspot by the focusing lens so that they are converged to the individualconvex arcuate faces formed on the surface of the solid-state lasermedium. Consequently, they are introduced into the inside of the lasermedium through the convex arcuate faces.

3. Optical Device having Zigzag Optical Path

Of the optical devices described hereinabove, the optical device whichis characterized in that, as shown in FIGS. 20 to 22, it is formed froma light transmitting optical material having a first face and a secondface opposing to each other and has a plurality of first reflectingportions provided on the first face and a plurality of second reflectingportions provided on the second face individually in an opposingrelationship to the first reflecting portions and further has a zigzagoptical path which is provided between the first reflecting portions andthe second reflecting portions and alternately couples the firstreflecting portions and the second reflecting portions to each other,and each of at least ones of the first reflecting portions and thesecond reflecting portions is a reflecting portion formed by coating areflecting film on a convex arcuate face, has an optical path of a greatlength and can be used, for example, as a higher harmonic convertingdevice.

A window for passing light therethrough is provided at each of an endportion of the first face and an opposite end portion of the secondface. One of the windows will be hereinafter referred to as incidencewindow, and the other will be hereinafter referred as outputting window.Light introduced into the light transmitting optical material throughthe incidence window passes the zigzag optical path described above andoutputs through the output window. The input window and the outputwindow may be provided at the opposite end portions of one of the faces(FIG. 24).

As an optical device having a zigzag optical path, an optical device canbe listed wherein a convex arcuate face is formed on a first one of apair of opposing faces of a light transmitting optical material and thesecond face is formed as a flat face as shown in FIGS. 20 and 21.Further, such junction type devices as shown in FIGS. 27 and 28 can belisted. Further, a higher harmonic wave converting device can be listedwhich is characterized in that, as shown in FIG. 22, a first convex artface is provided on one of a pair of opposing faces of a lighttransmitting optical material while a second convex arcuate face isprovided on the other face, and coatings are provided on both faces anda window is formed at an end portion of each of the faces.

Preferably, each of the convex arcuate faces is a generally sphericalface or aspherical face, for example, a face of an ellipsoid ofrevolution. In this instance, the spherical face or aspherical face mayhave distortion wherein the radius of curvature varies continuously orstepwise in a radial direction.

Upon formation of the convex arcuate faces, the error in formation ofthe convex arcuate faces can be corrected by making a plurality of setsof convex arcuate faces having radii of curvature which are different bya small amount from each other, effecting laser oscillation or higherharmonic conversion using a laser oscillator and selecting a set ofconvex arcuate faces with which the oscillation efficiency or the higherharmonic conversion efficiency is the highest. The diameter, the radiusof curvature and so forth of the convex arcuate faces are suitably setdepending upon an object of use, a wavelength and so forth of theoptical device. Formation of the convex arcuate faces may be performedsimilarly as described hereinabove.

While the first reflecting portions and the second reflecting portionsdescribed above are constructed, preferably for the maintenance of alight converging condition and the enhancement of the power intensity ofthe inside, such that a convex arcuate face such as a spherical case isformed at least on one face and part or all of a reflecting portion isformed from a reflecting mirror provided by the convex arcuate face(FIGS. 20 to 22), the two reflecting portions may be in the form of flatfaces (FIGS. 23 to 25). Further, a prism may be provided as a reflectingportion in place of a convex arcuate face (FIG. 26). In order to form aprism on an optical material, at an exposing step wherein a photoresistfilm is exposed to light of a circular or elliptic pattern in thephotolithography method described above, the distribution of theexposure light intensity should be varied in accordance with a profileof the prism.

The reflecting portions and windows can be formed by coating a totalreflecting film for light on a surface of a light transmitting opticalmaterial at locations at which the respective reflecting portions are tobe provided while no coating is provided at locations at which thewindows are to be provided (FIGS. 20, 25 and etc.). Or else, they can beformed by coating a total reflecting film for light on an entire face ofeach of the first and second faces and then removing the coatings atlocations of the windows. Further, coating may be performed only foreach of the reflecting portions (FIGS. 23 and 24).

As a method of such coating, a method wherein two kinds of thin filmshaving different refractive indexes are layered, by vacuum vapordeposition or sputtering, alternately to such thicknesses with which theoptical lengths at an aimed reflecting wavelength correspond to the ½wavelength can be listed.

As a method of removing the coatings, a method wherein coating isperformed in a condition wherein, for example, a photoresist film isformed at each window portion and the coatings are removed together withthe photoresist film or another method wherein a photoresist film isformed after application of a coating and then exposure and developmentare performed to remove the photoresist at each window portion,whereafter the exposed coating is removed by dry etching, can be listed.

Subsequently, an example of coating and formation of an incidence windowand an output window will be described in detail.

Photoresist is spin coated on a surface of a light transmitting opticalmaterial, and pre-baking is performed to form a photoresist film.Subsequently, a photomask having a circular light intercepting patternis closely contacted with a surface of the photoresist and ultravioletrays are irradiated upon the photoresist film to effect close contactexposure of the photoresist film. The photoresist film exposed toultraviolet rays is developed and then rinsed with pure water,whereafter it is dried. The photoresist film is first dried for 30minutes in a clean oven at 100° C. and then, post-baking is performedfor an hour in another clean oven at 175° C. Dry etching of the lighttransmitting optical material Wherein a convex arcuate face is made ofthe photoresist in this manner is performed using a dry etchingequipment to transfer the convex arcuate face made of the photoresist tothe surface of the light transmitting optical material.

Coating on the surface and formation of a window in the lighttransmitting optical material on which the convex arcuate face or noconvex arcuate face is formed in this manner is performed, for example,in the following manner. Prior to coating, photoresist is spin coated onthe surface of the light transmitting optical material and pre-baking isperformed to form a photoresist film, and then the photoresist is leftonly at each window portion by close contact exposure and developingprocessing. In this condition, TiO₂ and SiO₂ are alternately vapordeposited by an electron beam by means of an electron beam vapordepositing apparatus. Preferably, a coated film is such a film thatreflects almost all of light of frequencies between a basic wave and ahigher harmonic wave. After the specimen is taken out of the vapordepositing apparatus, it is soaked in acetone and washed using anultrasonic washing machine to remove the photoresist and the coated filmdeposited on the photoresist film to form a window. Further,formation,of a window is possible not only by the so-called lift-offmethod described above but also by etching. A method can be listedwherein, after coating is performed, spin coating and pre-baking areperformed for the photoresist to form a photoresist film, whereafterexposure, development and water washing are performed using a photomaskto expose the window portion through the photoresist film, and then,part or all of the coated film is removed by dry etching to form awindow. If coating for prevention of reflection is performed afterformation of the window portion, then an element of a further highperformance can be manufactured.

Light introduced into the incidence window of the optical deviceobtained in this manner is repetitively reflected alternately by the tworeflecting portions such that it advances in a zigzag pattern and thenoutputs through the output window. Since, due to such an action, it ispossible to assure a great optical path length and a beam can besuccessively converged by a light converging effect of the concavemirrors, the optical device can be utilized as a higher harmonic waveconverting device for light, a laser oscillator such as a slab laser andso forth.

As the light transmitting optical material for use for an optical devicehaving such a great optical path length, laser materials such as Nd:YAG,Nd:YAB, Nd:Y₃Al₅O₁₂, Nd:YLiF₄, Nd:YVO₄, Nd:La₂Be₂O₅ and Nd:Y₃Al₃(BO₃)₄,non-linear materials such as KNbO₃, LiNbO₃ and KTiOPO₄ and amorphousmaterials such as BK7, composite quartz and glass can be listed.

Upon production of an optical device of the present invention, aplurality of optical devices can be produced readily at a low cost bycutting a light transmitting optical material after a plurality of setsof convex arcuate faces and windows are formed collectively.

4. Short Wavelength Laser Apparatus Employing Device Having ZigzagOptical Path

A short wavelength laser apparatus can be constructed by using anon-linear optical device on which reflecting portions and windows areformed in such a manner as described above as a higher harmonic waveconverting device and disposing the higher harmonic wave convertingdevice and an exciting laser oscillator such that laser light may beconverged to one of the windows formed on the higher harmonic waveconverting device.

Since laser light outputted from a laser oscillator is emitted normallywith a fixed angle, it is preferable to convert the laser light intoparallel light or converge the same into a spot using a focusing lens inaccordance with the necessity. Laser light outputted from the excitinglaser oscillator is converted into parallel light or converged into aspot by the focusing lens so that it is converged as a basic wave intothe incidence window of the higher harmonic wave converting device. Thefundamental wave is introduced into the higher harmonic wave convertingdevice through the incidence window and then repetitively reflected bythe two reflecting portions of the higher harmonic wave convertingdevice so that it is added into a higher harmonic, and finally, thebasic wave and higher harmonic wave are outputted from the outputwindow.

Further, by employing a laser diode as the laser oscillator, a shortwavelength laser apparatus which is small in size, simple and convenientand can effect direct modulation can be constructed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-1 d are schematic diagrammatic views showing different stepsof an example of manufacturing method for an optical device of thepresent invention;

FIGS. 2 a-2 d are schematic diagrammatic views showing different stepsof another example of manufacturing method for an optical device of thepresent invention;

FIGS. 3 a-3 d are schematic diagrammatic views showing different stepsof a further example of manufacturing method for an optical device ofthe present invention;

FIGS. 4 a-4 e are schematic diagrammatic views showing different stepsof a still further example of manufacturing method for an optical deviceof the present invention;

FIG. 5 is a perspective view of a laser medium on which a convex arcuateface is formed;

FIG. 6 is a sectional view of a laser resonator wherein a convex arcuateface is formed integrally on each of the opposite faces of a lasermedium;

FIG. 7 is a sectional view of another laser resonator wherein a convexarcuate face is formed integrally on an end face of a laser medium;

FIG. 8 is a perspective view of an optical device;

FIG. 9 is a perspective view of another optical device;

FIG. 10 is a perspective view of a microlens;

FIG. 11 is a sectional view of the microlens;

FIG. 12 is a sectional view of an example of two-material Junction typelaser resonator wherein a convex arcuate face is formed on each of theopposite end faces;

FIG. 13 is a sectional view of another example of two-material Junctiontype laser resonator wherein a convex arcuate face is formed on an endface;

FIG. 14 is a diagram illustrating comparison between the speeds ofetching of a photoresist film and a glass substrate when theaccelerating voltage is varied as a dry etching condition;

FIG. 15 is a top plan view of an example of photomask used forproduction of an optical device of the ring laser type;

FIGS. 16 a-16 c are schematic views illustrating a cutting procedureemployed for production of the optical device of the ring laser type;

FIG. 17 is an illustrative view showing an optical path in the opticaldevice of the ring laser type;

FIGS. 18 a-18 b are schematic diagrammatic views illustrating a faultremoving method for a mirror face polished face according to the presentinvention;

FIG. 19 is a schematic view showing an example of optical system whichemploys an optical device of the ring laser type of the presentinvention;

FIGS. 20 and 21 are diagrammatic sectional views showing examples ofoptical device which have a convex arcuate face on a face thereof andhave a zigzag optical path;

FIG. 22 is a diagrammatic sectional view showing another example ofoptical device which has convex arcuate faces on the both faces opposingto each other and has a zigzag optical path;

FIGS. 23, 24 and 25 are diagrammatic sectional views showing furtherexamples of optical device which have reflecting portions each in theform of a flat plate and have a zigzag optical path;

FIG. 26 is a diagrammatic sectional showing an optical device which hasa reflecting portion formed from prisms and has a zigzag optical path;

FIGS. 27 and 28 are diagrammatic sectional views of optical deviceswherein two materials are joined to each other and convex arcuate facesare formed on one and both of the faces opposing to each other,respectively;

FIG. 29 is a perspective view showing an example of optical devicehaving a zigzag optical path;

FIG. 30 is a schematic view showing an example of short wavelength laserapparatus which employs an optical device of the present invention;

FIG. 31 is a schematic view showing an example of laser apparatus of thearray type of the present invention;

FIG. 32 is a schematic view showing an apparatus for observation of anear-field pattern;

FIG. 33 is a diagrammatic view showing a near-field pattern when laseroscillation is performed with the apparatus of FIG. 32;

FIG. 34 is a schematic view showing another example of laser apparatusof the array type of the present invention;

FIG. 35 is a schematic view showing another example of laser apparatusof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Part of an example of optical device of the present invention is shownin perspective view in FIG. 5. Referring to FIG. 5, reference numeral 10denotes a laser resonator, and 12 a generally spherical convex arcuateface formed on an end face of the laser resonator 10. The laserresonator 10 is constructed such that, as shown in FIG. 6, a firstconvex arcuate face 12 a is formed integrally on an end face of a lasermedium 11 while a second convex arcuate face 12 b is formed integrallyon the other end face of the laser medium 11, and a total reflectingfilm 13 which totally reflects laser light is provided on the firstconvex arcuate face 12 a while a semi-transmitting film 14 whichreflects part of laser light but transmits part of the laser lighttherethrough is formed on the second convex arcuate face 12 b. Thepresent construction is common not only to laser oscillators but also tonon-linear optical devices.

Part of another example of optical device of the present invention isshown in perspective view in FIG. 8. Referring to FIG. 8, referencenumeral 20 denotes an optical device, and 12 a generally sphericalconvex arcuate face. A plurality of such generally spherical convexarcuate faces 12 are formed on an end face of the optical device 20.FIG. 9 shows a modified arrangement wherein a plurality of convexarcuate faces 12 are connected to each other.

A further example of optical device of the present invention is shown insectional view in FIGS. 11 and 12. Referring to FIGS. 10 and 11,reference numeral 12 denotes a generally spherical convex arcuate face.A plurality of such generally spherical convex arcuate faces 12 areprovided and constitute a microlens.

Sectional views of an optical device having a zigzag optical path of thepresent invention are shown in FIGS. 20 to 28. A short wavelength laserapparatus which employs such an optical device as a higher harmonic waveconverting device is shown in FIG. 30.

An example of a laser apparatus of the array type of the presentinvention is shown in FIG. 31, FIG. 32 and another example is shown inFIG. 34.

In the following, a method of manufacturing an optical device of thepresent invention and a laser apparatus which employs the optical devicewill be described in connection with several examples with reference tothe drawings. According to the following examples, a convex arcuate faceor a concave arcuate face 12 can be formed on an optical material in thevarious devices described above. Normally, a plurality of convex arcuatefaces 12 or the like are formed on an optical material having a somewhatgreat area, and they are used as they are as optical devices or they arecut for each convex arcuate face 12 and so forth to form an opticaldevice.

EXAMPLE 1

First, a first example of method of manufacturing an optical device ofthe present invention will be described with reference to FIGS. 1 a-1 d.

A glass substrate 40 was used as an optical material on which a convexarcuate face 12 was to be formed. Photoresist OFPR800 made by Tokyo OhkaKogyo Kabushiki Kaisha. was spin coated on a surface of the glasssubstrate 40, and then the glass substrate 40 was pre-baked to form aphotoresist film 42 of 0.6 μm thick (refer to FIG. 1 a).

Subsequently, using as an exposing apparatus an enlarging machine 50 ofthe model CF670 made by Fuji Shashin Film Kabushiki Kaisha. in which aFUJINON EX 50 mm lens set to F4 was mounted, the enlarging machine wasadjusted such that the size of a pattern formed on an exposure negative52 and the size of an image of the pattern might have the ratio of 1:1.It is to be noted that, though not shown, an upper lamp house wasremoved and a cold mirror of the center wavelength of 400 nm wasmounted, and then an extra-high pressure mercury lamp was set to a lamphouse of the model UIS-5100 made by Ushio Denki-Kabushiki Kaisha so thatultraviolet rays were introduced as an exposure light source into thelamp house. The pattern of the negative 52 was a circular pattern.

The glass substrate 40 on which the photoresist film 42 was formed wasset to a focus position (refer to FIG. 1 b), and ultraviolet rays wereirradiated upon the glass substrate 40 to form, on the photoresist film42, an image of the pattern formed on the negative 52, whereafter thephotoresist film 42 was developed. Consequently, the photoresist film 42of a circular shape having a diameter of 100 μm remained on the surfaceof the glass substrate 40 as shown in FIG. 1 c. The surface of thecircular photoresist film 42 had a generally spherical shape and theradius of curvature of the surface was about 2 mm.

When a lens having a low resolution such as that in an enlarging machinefor a photographic film is used, the amount of ultraviolet raysirradiated upon the photoresist film 42 increases from a central portiontoward a peripheral portion of each circular pattern. Therefore, if thephotoresist film 42 on which images of patterns are formed aredeveloped, then the thickness of the photoresist film 42 remaining onthe surface of the glass substrate 40 decreases from a central portionto a peripheral portion of each circular pattern. Accordingly, thesurface of the photoresist film 42 after development presents agenerally spherical profile.

It is to be noted that, when the glass substrate 40 on which thephotoresist film 42 was formed was set to a position displaced by 3 mmfrom the focus position and then similar processing was performed, thephotoresist film 42 of a circular shape having a diameter of 60 μm wasleft on the surface of the glass substrate 40. The surface of thecircular photoresist 42 had a generally spherical profile and the radiusof curvature of the spherical face was about 1.5 mm.

Further, when a white circular shape pattern was photographed in asomewhat defocused condition to obtain a negative film having a circularpattern wherein a circular central portion is black and thephotographing density decreases toward an outer periphery and thenegative film was used as the negative 52 for circular pattern transfer,a semi-spherical photoresist pattern was formed without particularlyeffecting a defocusing operation for the glass substrate 40.

The glass substrate 40 obtained in this manner and having the circularphotoresist film 42 of the diameter of 100 μm formed thereon was dryetched using a dry etching equipment of the model ECR-310 made byNichiden Aneruba Kabushiki Kaisha. Dry etching conditions were suchthat, after the dry etching equipment was exhausted to 6.5×10⁻⁴ Pa, C₂F₆was introduced by 5 SCCM (Standard cubic Centimeter Minute) into theequipment, and etching was performed for one hour at the high frequencyoutput of 300 W, the enclosing magnetic field of 10⁻² T and the ionaccelerating voltage of 500 V.

By the dry etching under the conditions, the photoresist film 42 formedon the surface of the glass substrate 40 was etched and disappearedcompletely. Simultaneously, also the glass substrate 40 was etched sothat a convex arcuate face 12 having a generally spherical shape havingthe diameter of about 100 μm and the radius of curvature of about 4 mmwas formed on the surface of the glass substrate 40 (refer to FIG. 1 d).The reason why the radius of curvature of the convex arcuate face 12formed on the surface of the glass substrate 40 and the radius ofcurvature of the surface of the photoresist film 42 are different fromeach other is that the etching rates at the glass substrate 40 and thephotoresist. film 42 are different from each other.

EXAMPLE 2

Subsequently, a second example of method of manufacturing an opticaldevice of the present invention will be described.

A glass substrate 40 was used as an optical material on which a convexarcuate face 12 was to be formed. Photoresist OFPR800 made by Tokyo OhkaKogyo Kabushiki Kaisha. was spin coated on a surface of the glasssubstrate 40, and then the glass substrate 40 was pre-baked to form aphotoresist film 42 of 0.6 μm thick (refer to FIG. 2 a). Using a maskaligner of the model QUINTEL Q6000, the photoresist film 42 was exposedto light in a condition wherein the distance between the photomask 60and the photoresist film 42 was kept equal to 20 μm (refer to FIG. 2 b).

It is to be noted that, in this instance, a diffuser 62 (DFSQ-50C02-1500made by Siguma Koki) obtained by sand-blasting of the opposite faces ofan optical glass substrate BK7 of 1 mm thick with abrasive grain ofalumina of #1500 was placed on the photomask 60 so that diffused lighthaving passed through the diffuser 62 might be irradiated upon thephotoresist film 42 on the glass substrate 40 through the photomask 60.In this instance, the photomask 60 used was made of sodium lime glass, 4inches square and 0.09 inches thick and had a circular pattern having adiameter equal to or smaller than 100 μm.

Subsequently, development of the photoresist film 42 was performed usingdeveloper NMD-3 made by Tokyo Ohka Kogyo Kabushiki Kaisha. Afterdevelopment and rinsing with pure water, the photoresist film 42 of acircular pattern having a diameter equal to or smaller than 100 μmremained on the glass substrate 40 (refer to FIG. 2 b).

The surface of the photoresist film 42 was a convex arcuate face 42 a ofa substantially spherical shape having the radius of curvature of about4 mm. In this manner, the circular photoresist film 42 having thegenerally spherical convex arcuate face 42 a was able to be formed byusing diffused light with a suitable distance left between the photomask60 and the photoresist film 42 in this manner.

The glass substrate 40 obtained in this manner was dry etched using thedry etching equipment of the model ECR-310 E made by Nichiden AnerubaKabushiki Kaisha. Dry etching conditions were such that, after the dryetching equipment was exhausted to 6.5×10⁻⁴ Pa, C₂F₆ was introduced by 5SCCM into the equipment, and etching was performed for 20 minutes at thehigh frequency output of 300 W, the enclosing magnetic field of 10⁻² Tand the ion accelerating voltage of 700 V.

By the dry etching under the conditions, the photoresist film 42 formedon the surface of the glass substrate 40 was etched and disappearedcompletely. Simultaneously, also the glass substrate 40 was etched sothat a convex arcuate face 12 having a generally spherical shape havingthe diameter of about 100 μm and the radius of curvature of about 4 mmwas formed on the surface of the glass substrate 40 (refer to FIG. 2 d).

EXAMPLE 3

A case wherein the black and white are reversed is shown in (a) to referto FIGS. 3 a-3 d. In this instance, a generally spherical concavearcuate face 12 c having the diameter of 100 μm and the radius ofcurvature of about 4 mm was formed similarly to the case of the Example2.

EXAMPLE 4

Further, a fourth example of method of manufacturing an optical deviceof the present invention will be described.

A photoresist film 42 of 15 μm thick was formed on a glass substrate 40,and while the distance between a photomask 60 and the photoresist film42 was held equal to 8 mm, the photoresist film 42 was exposed to lightusing the photomask 60 having a circular pattern of the diameter of 1mm, whereafter development was performed under the same conditions as inthe second example so that the photoresist film 42 of a circular profilewas left on a surface of the glass substrate 40. The diameter of thephotoresist film 42 thus left was 0.8 mm and the radius of curvature ofthe surface was about 8 mm. The glass substrate 40 was dry etchedsimilarly as in the second example. However, the etching time was 8hours. A convex arcuate face 12 of a substantially spherical profilehaving the diameter of 0.8 mm and the radius of curvature of 8 mm wasformed on the surface of the glass substrate 40 after etching.

The ratio between the etching rates at the photoresist film 42 and theglass substrate 40 can be varied by varying a dry etching condition suchas, for example, the amount of gas to be introduced into the dry etchingequipment, the accelerating voltage or the like. Consequently, even ifthe radius of curvature of the convex arcuate face 42 a of thephotoresist film 42 left on the glass substrate 40 is equal, the radiusof curvature of the convex arcuate face 12 of the surface of the glasssubstrate 40 after dry etching can be varied. For example, when theglass substrate 40 on which the photoresist film 42 having the generallyspherical convex arcuate face 42 a having the diameter of 100 μm and theradius of curvature of about 4 mm was dry etched in accordance with thefollowing dry etching conditions, the radii of curvature of thegenerally spherical convex arcuate faces 12 on the surface of the glasssubstrate 40 obtained were such as described below.

Gas Used C₂F₆ C₂F₆ Quantity of Gas (SCCM) 3 10 High Frequency Output (W)300 300 Enclosing Magnet Field (T) 10⁻² 10⁻² Ion Accelerating Voltage(V) 700 300 Etching Time 45 min. 75 min. Radius of Curvature of 2.8 5.6Spherical Convex Arcuate Face on Surface of Glass Substrate (mm)

EXAMPLE 5

Further, a fifth embodiment of method of manufacturing an optical deviceof the present invention will be described.

A glass substrate 40 was used as an optical material on which a convexarcuate face 12 was to be formed. Photoresist OFPR800 made by Tokyo OhkaKogyo Kabushiki Kaisha. was spin coated on a surface of the glasssubstrate, and then the glass substrate was pre-baked to form aphotoresist film 42 of 8 μm thick (refer to FIG. 4 a).

Subsequently, by a so-called close contact exposure method wherein aphotomask 60 was closely contacted with the photoresist film 42, thephotoresist film 42 was exposed to light through the photo mask with acircular pattern of the diameter of 100 μm (refer to FIG. 4 c). Thephotoresist film 42 was developed using developer NMD-3 made by TokyoOka Kogyo Kabushiki Kaisha and then rinsed with pure water. Thephotoresist film 42 of a column-shaped profile of the diameter of 100 μmremained on the glass substrate 40 ((c) of FIG. 4).

The glass substrate 40 was placed for 30 minutes in a clean oven of 175°C. Since the photoresist film 42 was held at a temperature higher than aglass transition point of the material constituting the photoresist film42, part of it was thermally fluidized so that it was deformed into aliquid drop so that a generally spherical convex arcuate face 42 ahaving the radius of curvature of about 100 μm was formed (refer to FIG.4 d). The heating conditions for the photoresist film 42 must only be atemperature higher than a glass transition point of the materialconstituting the photoresist film 42 and a time sufficient for part ofthe photoresist film 42 to be thermally fluidized.

The glass substrate 40 obtained in this manner was dry etched using thedry etching equipment of the model ECR-310 E made by Nichiden AnerubaKabushiki Kaisha. Dry etching conditions were such that, after the dryetching equipment was exhausted to 6.5×10⁻⁴ Pa, oxygen was introduced by5 SCCM into the equipment, and etching was performed for 1 hour at thehigh frequency output of 300 W, the enclosing magnetic field of 10⁻² Tand the ion accelerating voltage of 500 V.

By the dry etching under the conditions, the photoresist film 42 formedon the surface of the glass substrate 40 was etched and disappearedcompletely. Simultaneously, also the glass substrate 40 was etched sothat a convex arcuate face 12 having a generally spherical shape havingthe diameter of about 100 μm and the radius of curvature of about 5 mmwas formed on the surface of the glass substrate 40 (refer to FIG. 4 e).

The etching rate can be varied by varying the ion accelerating voltage,and at the accelerating voltages of 300 V and 700 V, the radius ofcurvature of the generally spherical convex arcuate face 12 on thesurface of the glass substrate 40 was about 10 and 2.5 mm, respectively.

Further, when not a circular shape but an elliptic shape is used for apattern of the photomask 60, the convex arcuate face 12 to be formedfinally on the surface of the glass substrate 40 does not have aspherical shape but has a shape of a face of an ellipsoid of revolution,but also the convex arcuate face 12 of such a shape of a face of anellipsoid of revolution was able to be formed readily by the method ofthe example described above.

EXAMPLE 6

A convex arcuate face 12 was formed on a surface of a glass substrate 40by a method similar to that of the Example 4 except that the pattern ofthe photomask 60 was an elliptic shape having the major diameter of 150μm and the miner diameter of 75 μm. When the ion accelerating voltagewas set to 500 V, the convex arcuate face 12 on the surface of the glasssubstrate 40 obtained had the shape of a face of an ellipsoid ofrevolution having the radius of curvature of about 11.3 mm on the majordiameter side and the radius of curvature of about 2.8 mm on the minordiameter side.

With an optical material other than the glass substrate 40, for example,with such a material as KNbO₃ or Nd:Y₃Al₅O₁₂, when the etching rate isdifferent from that of the glass substrate 40, a convex arcuate face 12or a concave arcuate face can be formed readily on a surface of the sameby a method similar to those of the Examples 1 to 6 described above.

EXAMPLE 7

The present example is an example wherein it was tested to see in whatmanner a spherical convex arcuate face of a glass substrate afteretching varies when an etching condition is varied continuously duringetching using photoresist, on which a spherical face is formed, as amask. First, a generally spherical convex arcuate face 42 a having theradius of curvature of about 100 μm was formed on a glass substrate 40similarly as in the Example 5 except that the photoresist film 42 wasformed with the thickness of 6 μm.

Subsequently, the glass substrate 40 on which the false spherical facewas formed from the photoresist in this manner was set to the dryetching equipment of the model ECR-310 E made by Nichiden AnerubaKabushiki Kaisha. and exhausted to 6.5×10⁻⁴ Pa, and then oxygen wasintroduced by 5 SCCM into the dry etching equipment. Thus, etching wasperformed for one hour and thirty minutes at the high frequency outputof 300 W and the enclosing magnetic field of 10⁻² T while decreasing theion accelerating voltage at the rate of 1 V/minute from 500 V.

In this instance, the photoresist disappeared completely, and theprofile of the photoresist was transferred to the glass substrate sothat a spherical face having some deformation wherein the diameter wasabout 100 μm and the radius of curvature was 5 mm at a central portionand 4.3 mm at a peripheral portion was produced.

FIG. 14 shows a relationship between the accelerating voltage (X-axis)and the ratio between the etching rates at the photoresist OFPR800 madeby Tokyo Ohka Kogyo Kabushiki Kaisha and the BK7 glass substrate in theECR-310 E equipment when the glass substrate is etched using thephotoresist as a mask. As apparently seen from FIG. 14, if an etchingcondition is varied continuously during etching, arbitrary distortion ina radial direction can be provided to a spherical face of the glasssubstrate.

While, in the present example, the accelerating voltage was continuouslyvaried to control the profile of the spherical face after etching, asimilar effect is obtained if not the accelerating voltage but someother parameter such as the gas flow rate or the high frequency outputis varied. Further, even if a parameter is varied not continuously butstepwise, a spherical face having stepwise distortion in a radialdirection is obtained.

When the profile of the spherical face after development and rinsing isan elliptic column-shaped profile, an aspherical elliptic lens which ismost suitable for convergency of light of a laser diode can bemanufactured by this method.

According to this method, an etching condition can be varied duringetching to form an aspherical face having an arbitrary degree ofdistortion from a spherical face.

EXAMPLE 8

The present example is an example wherein faults by polishing abrasivegrain upon mirror face polishing of an optical material are removed bydry etching.

KNbO₃ single crystal was used as an optical material on which a convexarcuate face 12 was to be formed. While the forming method itself of theconvex arcuate face 12 was substantially same as in the Example 5, aphotomask having a plurality of circular patterns like 2 dimensionalarray thereof as shown in FIG. 15 was used as a photomask 60. Afterclose contact exposure was performed similarly as in the Example 5 usingthe KNbO₃ single crystal piece in place of a glass substrate and usingthe photomask having the plurality of circular patterns thereon in thismanner, development with NMD-3 developer and rinsing with pure waterwere performed to form a plurality of photoresist films of acolumn-shaped profile having the diameter of 100 μm corresponding to thecircular patterns on the single crystal piece. Subsequently, the singlecrystal piece was thermally heated in the clean oven similarly as in theExample 5 and then dry etched using the dry etching equipment of themodel ECR-310 E made by Nichiden Aneruba Kabushiki Kaisha. By theoperation under the dry etching conditions described above, a pluralityof generally spherical convex arcuate faces 12 having the diameter ofabout 100 μm and the radius of curvature of about 6.0 mm were formed ona surface a of the KNbO₃ single crystal piece 70.

Subsequently, a dielectric multi-layer film made of SiO₂ and TiO₂ wascoated by vapor deposition on the face a of the single crystal piece 70to form a total reflecting film (transmission factor 4% with thewavelength of 860 nm, reflection factor 99.5% with the wavelength of 430nm) (not shown), and another dielectric multi-layer film was coated onanother face b of the single crystal piece 70 to form asemi-transmitting film (reflection factor 99.5% with the wavelength of860 nm, transmission factor 80% with the wavelength of 430 nm) (notshown). After then, the face c side of the single crystal piece 70 wasfirst cut as shown in refer to FIG. 16 b and then the cut face waspolished successively using polishing grains GC #1000, #2000, #3000 and#4000 made by Fujimi Kenmazai Kogyo Kabushiki Kaisha. and then polishedinto a mirror face similarly using Compol-EX made by Fujimi KenmazaiKogyo Kabushiki Kaisha. After then, a portion of the single crystalpiece 70 for one resonator was cut as shown in FIG. 16 b to make anon-linear optical device of the ring laser type.

In the present condition, the face c of the optical device was not aperfect mirror face, and when it was observed using a differentialinterference microscope, faults by polishing were found. If the face chas no fault thereon, then part of light introduced into such an opticaldevice through the lens 12 is, as shown in FIG. 17 (in the figure, fullline arrow marks denote incidence light, broken line arrow marks denotetransmission light, reference 80 denotes a fault on the face c shownschematically, 13 a total reflecting film, and 14 a semi-transmittingfilm), reflected by the face b as indicated by the solid line arrowmarks and the reflected light is all returned to the lens 12 again.However, since the polished face c has a fault 80 thereon, the reflectedlight is scattered at the portion of the fault 80, and consequently,part of the incidence light will not be returned to the lens 12.However, according to the present invention, such polish faults can beeliminated by the following method.

First, after the cutting and polishing the face c of the crystal piece70 in a condition shown in (b) of FIG. 16, photoresist OFPR800 made byTokyo Ohka Kogyo Kabushiki Kaisha. was spin coated on the face c,whereafter the crystal piece 70 was pre-baked to form a photoresist film42 having a film thickness of 600 nm. Subsequently, the photoresist film42 (and the face c of the crystal piece 70) were etched using the dryetching equipment of the model ECR310 made by Nichiden Aneruba KabushikiKaisha. Etching conditions were such that, after the dry etchingequipment was exhausted to 6.5×10⁻⁴ Pa, C₂F₆ was introduced by 5 SCCMinto the equipment, and etching was performed at the high frequencyoutput of 300 W, the enclosing magnetic field of 10⁻² T and the ionaccelerating voltage of 700 V.

When etching was performed for 30 minutes under the conditions, thephotoresist disappeared completely. After then, etching was continuedunder the same conditions, and after etching for a total of 3 hours, thecrystal piece 70 was taken out. The surface of the crystal was etched byabout 3 μm, and by observation of the differential interferencemicroscope, faults by polishing which were observed before etchingdisappeared and an almost perfect mirror face was obtained as shown inFIG. 18 b. After then, the crystal piece 70 was cut in a profile shownin FIG. 16 c.

Meanwhile, it is also possible to apply such processing in advance tothe face b shown in FIG. 16 a.

Subsequently, the optical device from which faults had been removed inthis manner was set as an optical device 95 on a non-linear opticalsystem for SHG generation shown in FIG. 19 and was excited with thewavelength of 862 nm from its spherical face side using a laser diodeSLD 7033101 made by Sanyo Electric Co., Ltd. Consequently, an output ofthe wavelength of 431 nm was obtained with 5 mW at the highest. It is tobe noted that reference numeral 90 in FIG. 19 denotes the laser diode,91 a converging lens F-L40B made by New Port Co., 92 a cylindrical lenspair for shaping a beam (aspect ratio 1:2), 93 a Faraday isolatorISO-7885 made by New Port Co., and 94 a converging lens (f=62.9 mm,plano-convex lens).

The optical devices on which convex arcuate faces are formed in theExamples 1 to 8 described so far can be used as optical devices having azigzag optical path by applying a coating to them and providing areflecting portion and a window portion to them.

EXAMPLE 9

Subsequently, an example of laser apparatus of the array type will bedescribed.

An outline of an example of laser apparatus of the present invention isshown in FIG. 31. The laser apparatus is constituted from a solid-statelaser resonator 10, a pair of focusing lenses 2 and 3 and a laser diode100 of the multi-stripe type serving as an exciting light source oflaser oscillation.

The laser diode 100 of the multi-stripe type is a GaAlAs laser diode ofthe double hetero type designed such that the oscillation wavelength maybe 809 nm, and has five active waveguides of 3 μm wide at an interval of100 μm. The focusing lenses 2 and 3 are focusing lenses F-L40B made byNew Port Co.

The solid-state laser resonator 10 is a laser rod made of Nd:YAG crystaland has five convex arcuate faces having the diameter of 95 μm and theradius of curvature of 7 mm formed on an end face thereof at a distanceof 100 μm on a straight line. A coating is formed on an incidence faceof the solid-state laser resonator 10 for exciting light such that thereflection factor at the wavelength of 1.06 μm may be 99.95% and thetransmission factor at the wavelength of 809 nm may be 83%, and anothercoating is formed on an opposing face of the solid-state laser resonator10 such that the reflection factor at the wavelength of 1.06 μm may be96.5% and the reflectionffactor at the wavelength of 809 nm may be99.8%. The length of the resonator is 3.75 mm.

Formation of the convex arcuate faces on the end face of the laser rodwas performed in the following manner.

Photoresist OFPR800 made by Tokyo Ohka Kogyo Kabushiki Kaisha. was spincoated on the end face of the laser rod (20 mm×20 mm×3.75 mm), and thenthe laser rod was pre-baked to form a photoresist film 42 of 0.6 μmthick (refer to FIG. 1 a).

Then, using as an exposure apparatus the enlarging machine 50 of themodel CF670 made by Fuji Shashin Film Kabushiki Kaisha. on which theFUJINON EX 50 mm lens set to F4 was mounted, the enlarging machine wasadjusted such that the ratio between the size of a pattern formed on anexposure negative 52 and the size of an image of the pattern might be1:1. It is to be noted that, though not shown, the upper lamp house wasremoved and the cold mirror of the center wavelength of 400 nm wasmounted, and then the extra-high pressure mercury lamp was set to thelamp house of the model UIS-5100 made by Ushio Kabushiki Kaisha so thatultraviolet rays were introduced as an exposure light source into thelamp house. The pattern of the negative 52 was a circular pattern.

The laser rod 40 on which the photoresist film 42 was formed was set toa focus position (refer to FIG. 1 b), and ultraviolet rays wereirradiated upon the laser rod 40 to form, on the photoresist film 42, animage of the pattern formed on the negative 52, whereafter thephotoresist film 42 was developed. Consequently, the photoresist films42 a of a circular shape having the diameter of 96 μm remained on thesurface of the laser rod 40 as shown in FIG. 1 c. The surface of eachcircular photoresist film 42 a had a generally spherical shape and theradius of curvature of the surface was about 5 mm.

When a lens having a low resolution such as that in an enlarging machinefor a photographic film is used, the amount of ultraviolet raysirradiated upon the photoresist film 42 increases from a central portiontoward a peripheral portion of each circular pattern. Therefore, if thephotoresist film 42 on which images of patterns are formed aredeveloped, then the thickness of the photoresist film 42 remaining onthe end face of the laser rod decreases from a central portion to aperipheral portion of each circular pattern. Accordingly, the surface ofthe photoresist film 42 after development presents a generally sphericalprofile.

It is to be noted that, when the laser rod 40 on which the photoresistfilm 42 was formed was set to a position displaced by 1.5 mm from thefocus position and then similar processing was performed, thephotoresist film 42 of a circular shape having the diameter of 60 μm wasleft on the surface of the laser rod 40. The surface of the circularphotoresist 42 had a generally spherical profile and the radius ofcurvature of the spherical face was about 12 mm.

Further, when a white circular shape pattern was photographed in asomewhat defocused condition to obtain a negative film having a circularpattern wherein a circular central portion is black and thephotographing density decreases toward an outer periphery and thenegative film was used as the negative 52 for circular pattern transfer,a semi-spherical photoresist pattern was formed without particularlydisplacing the focus position.

The laser rod 40 obtained in this manner and having the circularphotoresist film 42 of the diameter of 96 μm formed thereon was dryetched using the dry etching equipment of the model ECR-310 made byNichiden Aneruba Kabushiki Kaisha. Dry etching conditions were suchthat, after the dry etching equipment was exhausted to 6.5×10⁻⁴ Pa, C₂F₆was introduced by 5 SCCM (Standard Cubic Centimeter Minute) into theequipment, and etching was performed for one hour at the high frequencyoutput of 300 W, the enclosing magnetic field of 10⁻² T and the ionaccelerating voltage of 500 V.

By the dry etching under the conditions, the photoresist film 42 formedon the end face of the laser rod 40 was etched and disappearedcompletely. At the same time, also the laser rod 40 was etched so that aconvex arcuate face 12 having a generally spherical shape having thediameter of about 95 μm and the radius of curvature of about 7 mm wasformed on the end face of the laser rod 40 (refer to FIG. 1 d). Thereason why the radius of curvature of the convex arcuate face formed onthe end face of the laser rod and the radius of curvature of the surfaceof the photoresist film are different from each other is that theetching rates at them are different from each other.

The coating was performed such that, using a vacuum vapor depositingequipment, thin films of SiO₂ and TiO₂ optically corresponding to a ½wavelength were alternately layered. More particularly, on the incidenceface for exciting light, a film of SiO₂ of about 0.36 μm thick and afilm of TiO₂ of about 0.27 μm thick were alternately layered for 8cycles (a total of 16 layers). On the emergence face, a layer of SiO₂ ofabout 0.36 μm thick and a layer of TiO₂ of about 0.27 μm thick werealternately layered for 4 cycles (a total of 8 layers) and then a layerof SiO₂ of about 0.27 μm thick and a layer of TiO₂ of about 0.21 μmthick were alternately layered for 8 cycles (a total of 16 layers) as areflecting film for 810 nm.

The laser resonator 4 of the array type manufactured in this manner, thelaser diode 1 and the focusing lenses 2 and 3 are arranged such thatlaser light outputted from the laser diode 1 may be introduced into theconvex arcuate faces on the end face of the laser rod.

Subsequently, a near-field pattern of output light of the laserapparatus of the present invention was investigated.

Construction of an apparatus for observation of a near-field pattern isshown in FIG. 32. A laser diode (model SDL2432 made by SPECTRA DIODELABS.) of the multi-stripe type having the oscillation wavelength of 809nm was used as the exciting source, and a focusing lens F-L40B (focallength 4.8 mm) made by New Port Co. was used as the focusing lens 2 onthe exciting source side while a focusing lens AV1815 (focal length18.07 mm) made by Olympus Kabushiki Kaisha was used as the focusing lens3 on the laser resonator side.

The laser resonator 10 is a laser resonator wherein convex arcuate facesare formed on a Nd:YAG rod and coatings are applied to the opposite endfaces of the rod in a similar manner as described hereinabove, and threeconvex arcuate faces having the diameter of 95 μm and the radius ofcurvature of 7 mm are formed at an interval of 100 μm on the face of thelaser resonator on the focusing lens side.

They are arranged such that laser light outputted from the laser diode100 may be introduced into the convex arcuate faces on the end face ofthe laser rod, and further, as shown in FIG. 32, a filter 101 (modelITF-50S-100RM made by Siguma Koki) which attenuates exciting light ofthe wavelength of 809 nm but transmits therethrough the oscillationwavelength of 1.06 μm of the Nd:YAG crystal, a plano-convex lens (focallength 50 mm) 102 for observing a near-field pattern and a CCD element103 for a beam profiler not shown are disposed on the output side of thelaser rod.

The laser diode 1 has active waveguides at a distance of 10 μm over thewidth of 100 μm, and emitted rays of light over the width of 100 μm canbe enlarged to the width of 400 μm and projected to the three sphericalfaces by the focusing lenses 2 and 3 to excite the three spherical facesto obtain three laser beams. A near-field pattern when laser oscillationis performed with the apparatus described above is shown in FIG. 33.

As apparent from FIG. 33, is can be seen that three laser beams havingsimilar profiles are oscillated at the same time.

EXAMPLE 10

Subsequently, a second example of laser apparatus of the presentinvention is shown in FIG. 34. In the present example, four laser diodesof the single type are provided, and four optical fibers for guidinglaser light from the laser diodes are provided. The four optical fibersare bundled at end portions thereof and are opposed to a laser resonator10. The laser resonator 10 was manufactured similarly as in thepreceding example, and four convex arcuate faces are disposed, at an endface of a laser medium, at the four corners of a square corresponding tothe bundle of the four optical fibers. Further, a pair of focusinglenses 2 and 3 disposed between the optical fibers and the laseroscillator.

Action and effects of the present example are also similar to those ofthe preceding example.

EXAMPLE 11

Subsequently, an example of short wavelength laser apparatus wherein anoptical device having a zigzag optical path is employed as a higherharmonic wave converting device will be described.

An outline of construction of a higher harmonic wave converting deviceand a short wavelength laser apparatus according to the present exampleis shown in FIG. 30. Referring to FIG. 30, reference numeral 1 denotes alaser diode SLD7033101 made by SANYO Kabushiki Kaisha, 2 a focusing lensF-L40B made by New Port Co., 3 a plano-concave lens φ=25 mm, f=62.9 mm,and 10 a higher harmonic wave converting device according to the presentinvention obtained by polishing a face a of a single crystal piece ofKNbO₃, forming convex arcuate faces on one face, applying a highreflection coating on the one face and removing part of the coating.

Reference numeral 12 denotes a convex spherical face formed on a surfaceof the light transmitting optical material, 17 an incidence windowformed by removing part of the coated film in order to admit a basicwave into the light transmitting optical material, and 18 a higherharmonic wave outputting window formed by removing part of the coatedfilm in order to extract a higher harmonic wave from the lighttransmitting optical material. A broken line indicates an optic axis.

The coating is performed for the face of the light transmitting opticalmaterial having the convex spherical faces and another face opposing tothe face such that the reflection factor at the wavelength of 860 nm maybe 99.95% and the reflection factor at the wavelength of 430 nm may be99.9%.

A perspective view of a higher harmonic wave converting device actuallyproduced using KNbO₃ as a light transmitting optical material is shownin FIG. 29. The higher harmonic wave converting device was made in thefollowing manner.

Photoresist OFPR800 made by Tokyo Ohka Kogyo Kabushiki Kaisha was spincoated on a surface of the KNbO₃ material having a face a of 10 mm×10 mmand the thickness of 5 mm, and pre-baking was performed for thephotoresist film of 6 mm thick. Then, a photomask having circular lightintercepting patterns was closely contacted with a surface of thephotoresist film and ultraviolet rays were irradiated upon thephotoresist film to effect close contact exposure. In this instance, aplurality of combinations of circular patterns wherein the diameter wasvaried by small amounts among 104 μm, 102 μm, 100 μm, 98 μm and 96 μmwere disposed on the photomask. The sets of the individual diameterscorrespond to rows of convex spherical faces denoted by 4 to 8 in FIG.29.

The photoresist film exposed to ultraviolet rays was developed for oneminute with developer NMD-3 made by Tokyo Ohka Kogyo Kabushiki Kaishaand then rinsed with pure water, whereafter it was dried. Thephotoresist films each in the form of a round column remained on theKNbO₃ material. The KNbO₃ material was first dried for 30 minutes in theclean oven of 100° C. and then post-baked for one hour in the clean ovenof 175° C. As a result, generally spherical convex arcuate faces wereformed due to thermal fluidization.

The KNbO₃ material on the surface of which the spherical photoresist wasformed in this manner was dry etched using the dry etching equipment ofthe model ECR-310E made by Nichiden Aneruba Kabushiki Kaisha to transferthe convex spherical faces produced from the photoresist. In thisinstance, etching conditions were: etching gas, oxygen 5SCCM; microwaveinput 300 W; ion enclosing magnetic field 10⁻² T; and ion acceleratingvoltage 325 V.

The radii of curvature of the convex spherical faces produced in thismanner were 10.44 mm with the spherical faces produced from the patternof the diameter of 104 μm, and 10.26 mm, 10.12 mm, 9.96 mm and 9.80 mmwith the spherical faces produced from the patterns of the diameters of102 μm, 100 μm, 98 μm and 96 μm, respectively.

A high reflection coating consisting of TiO₂ and SiO₂ was applied toeach of the face on which the spherical faces were formed and theopposing face of each of the KNbO₃ single crystal blocks on which theconvex spherical faces had been formed in this manner. Prior to suchcoating, TSMR8900 photoresist made by Tokyo Ohka Kogyo Kabushiki Kaishawas first spin coated on the side of the KNbO₃ single crystal blocks onwhich the spherical faces were formed, and then pre-baking was performedto form a film of the thickness of 9 μm, whereafter the photoresist wasleft, by close contact exposure and developing processing, only at awindow portion through which a waveform was to be admitted.

In this condition, TiO₂ and SiO₂ were alternately electron beam vapordeposited by means of an electron beam vapor depositing apparatus of themodel EX-550 made by Nippon Shinku Kabushiki Kaisha so as to vapordeposit them for 6 cycles in 12 layers in a condition wherein a maximumreflection factor was obtained at the wavelength of 860 nm and then for12.5 cycles in 25 layers in another condition wherein a maximumreflection factor was obtained at the wavelength of 430 nm. The vapordeposition was performed intermittently so that the temperature of thespecimens might be equal to or lower than 160° C. to the highest. Thereflection factor of the coated films was 99.95% at the wavelength of860 nm and 99.9% at the wavelength of 430 nm.

After the specimens were taken out of the vapor depositing apparatus,they were immersed in acetone and washed using an ultrasonic washer toremove the photoresist and the coated films vapor deposited on thephotoresist to form incidence windows.

Subsequently, similar processing was applied also to the opposing faces,and coatings were provided and also higher harmonic wave output windowswere formed. Each of them was set such that such construction as shownin FIG. 30 might be obtained, and laser light of the wavelength of 862nm and the power of 78 mW was introduced into it such that the sphericalfaces having he radius of curvature of 10.12 mm might be used whilekeeping it at 31.7° C. As a result, a higher harmonic output of thewavelength of 431 nm and the power of 1.2 mW was obtained.

The short wavelength laser apparatus can also be arranged as shown inFIG. 35. As shown in this figure, the apparatus is provided with aplurality of exciting sources 330 for producing a plurality ofexcitation laser beams, and an optical block. The optical block includesat least a part of laser resonators 10′ that receive each of theexcitation laser beams and emitting emitted laser beams with differentwavelength from that of the excitation laser beams. The optical blockhas a first end face 310 and a second end face 340 disposed opposite thefirst end face 310. The first end face 310 includes a planar portion 350and a plurality of convex arcuate portions 300. An entire surface of thesecond end face 340 is substantially planar. An optical film coats atleast the convex arcuate portions 300.

The resonators further include totally reflective films 370 covering theconvex arcuate portions 300, a semi-transmitting mirror 360 covering aportion of the first end face 310 other than the convex arcuate portions300, and a plurality of optical films 320 coating at least a pluralityof portions on the second end face 340. The optical films 320 can be anyone of an anti-reflective film, a semi-transmitting mirror film, and atotally reflective film.

What is claimed is:
 1. An optical device, comprising: a lighttransmitting non-linear optical material or laser material having afirst face and a second face, said first and second faces opposing eachother, said first face having a plurality of first reflecting portionsprovided thereon, said second face having a plurality of secondreflecting portions provided thereon, each of said second reflectingportions corresponding to one of said first reflecting portions, saidfirst and second faces being substantially flat except for at least oneconvex arcuate portion being formed on at least one of said first andsecond faces, and at least one of said first and second reflectingportions being obtained by coating a reflective material on said arcuateportion.
 2. An optical device, comprising: a light transmittingnon-linear optical material or a laser material having a first face anda second face, said first and second face opposing each other, saidfirst face having a plurality of first reflecting portions providedthereon, said second face having a plurality of second reflectingportions provided thereon, each of said second reflecting portionscorresponding to one of said first reflecting portions, said first facehaving at least one convex arcuate portion and a flat portion parallelto said second face formed thereon, said at least one convex arcuateportion being coated with a first reflective material, said second facebeing flat and at least one of said second reflecting portions beingobtained by coating a second reflective material on said second face. 3.A laser apparatus, comprising: an exciting source producing at least oneexcitation laser beam; and a laser resonator receiving said at least oneexcitation laser beam, said laser resonator including, a lighttransmitting non-linear optical material or laser material having afirst face and a second face, said first and second face opposing eachother, said first face having a plurality of first reflecting portionsprovided thereon, said second face having a plurality of secondreflecting portions provided thereon, each of said second reflectingportions corresponding to one of said first reflecting portions, saidfirst and second faces being substantially flat except for at least oneconvex arcuate portion being formed on at least one of said first andsecond faces, and at least one of said first and second reflectingportions being obtained by coating a reflective material on said convexarcuate portion.
 4. The laser apparatus of claim 3, wherein saidexciting source produces a plurality of excitation laser beams and saidlaser resonator receives respective ones of said excitation laser beams,wherein said laser resonator includes said light transmitting non-linearoptical material or laser material having a plurality of convex arcuateportions formed on said one of said first and second faces which isflat.
 5. The laser apparatus of claim 4, wherein each of said convexarcuate portions receives a corresponding one of said excitation laserbeams.
 6. The laser apparatus of claim 4, wherein said exciting sourceincludes a semiconductor laser of a multistripe type which outputs aplurality of laser beams as said excitation laser beams.
 7. The laserapparatus of claim 4, wherein said exciting source includes a pluralityof laser producing devices, each of said laser producing devicesproducing a laser beam as an excitation laser beam, each of said laserproducing devices including an optical fiber which guides said laserbeam to a corresponding one of said plurality of convex arcuate portionsof said resonator.
 8. A laser apparatus of claim 3, wherein said lighttransmitting non-linear optical material or laser material is formedintegrally.
 9. An optical device of claim 3, wherein said first face andsaid second face are coated with a reflective material to form saidfirst and second reflecting portions, said reflective material eachhaving a window for receiving and outputting said at least oneexcitation beam.
 10. A laser apparatus, comprising: a plurality ofexciting sources producing a plurality of excitation laser beams; and anoptical block, wherein said optical block including at least a part oflaser resonators receiving each of said excitation laser beams andemitting emitted laser beams with different wavelength from that of theexcitation laser beams, and said optical block having a first end faceand a second end face disposed opposite said first end face, said firstend face including a planar portion and a plurality of convex arcuateportions, an entire surface of said second end face being substantiallyplanar, and optical film coating at least said convex arcuate portionson the first end face.
 11. The laser apparatus of claim 10, wherein saidoptical film coated on at least said convex arcuate portions being atotally reflective film, and an anti-reflective film coating at least aplurality of portions on said second end face.
 12. The laser apparatusof claim 11, wherein said laser resonators further includes asemi-transmitting mirror, coating a portion of said first end face otherthan said convex arcuate portions, opposed to said second end face. 13.The laser apparatus of claim 12, wherein said optical block is a lasermedium.
 14. The laser apparatus of claim 11, wherein said optical blockis a laser medium.
 15. The laser apparatus of claim 10, wherein saidoptical film coated on at least said convex arcuate portions being atotally reflective film, and a semi-transmitting mirror film coating atleast a plurality of portions on said second end face.
 16. The laserapparatus of claim 15, wherein said optical block is a laser medium. 17.The laser apparatus of claim 10, further comprising: a totallyreflective film coating at least a plurality of portions on said secondend face and said optical film coated on at least said convex arcuateportions being a semi-transmitting mirror.
 18. The laser apparatus ofclaim 17, wherein said optical block is a laser medium.
 19. The laserapparatus of claim 10, wherein said optical block is a non-linearoptical material.